The hierarchical porous carbons, those whose pore architecture is composed of large macroporous with additional mesoporous within the frameworks, have attracted much research attention because of their potential applications in many research fields such as catalysis, adsorbents, coating, sensors, separation and chemical filtration, microelectronics, electro-optics, supercapacitors, environmental engineering, insulators, biomaterials engineering and other energy-related applications. In this regard, several research approaches have already been done for the fabrication of macroporous with mesoporous (bimodal) carbon materials, as well as bimodal carbon composites, which are well summarized in several review articles [Yunpu Zhai et al., Advanced Materials, 2011, 23, 4828-4850; An-Hui Lu et al., Macromolecular Chemistry Physics, 2012, 213, 1107-1131; Chengdu Liang et al., Angewandte Chemie International Edition, 2008, 47, 3696-3717; A. Stein, Advanced Materials, 2003, 15, 763-775; Z. Y. Yuan and B. L. Su, J. Material Chemistry, 2006, 16, 663-677]. These bimodal carbon materials have advantages over the unimodal carbon materials (mesoporous or macroporous carbon) in terms of diffusion efficiency, high surface area and good conductivity.
However, it has been observed from the literature that most of the research articles have mainly been focused on the preparation of macroporous with mesoporous carbon materials with different forms like carbon powders, aerogel powder or particles, micro/macro-spheres, fibers and graphite powder [W. Sui et al., Materials Letters, 2011, 65, 2534-2536; Z. Wang et al., Carbon, 2008, 46, 1702-1710; C-H. Huang et al., Carbon, 2011, 49, 3055-3064; S. Lu and Y. Liu, Applied Catalysis B: Environmental, 2012, 111-112, 492-501; X. Lu et al., J. Chem. Biosensors and Bioelectronics, 2009, 25, 244-247]. The small particles, as well as powder forms, of the carbon materials might limit the applicability of these materials because these materials can create a high pressure drop.
Therefore, the research of carbon foams has become attractive to many researchers because of their unique characteristics such as very high porosity with interconnected porous network, low density, low pressure drop and high thermal conductivity which make it useful for various potential applications [J. Song et al., New Carbon Materials, 2012, 27 (1), 27-34; R. Narasimman and K. Prabhakaran, Carbon, 2012, 50, 1999-2009]. Their application includes thermal management, electrodes, catalyst supports, high temperature insulation, ablative materials, etc.
The carbon foams are mainly classified into three categories such as reticulated vitreous carbon foams (RVC), non-graphitic carbon foams and graphitic carbon foams. Reticulated vitreous carbon (RVC) as well as non-graphitic carbon foams are prepared by foaming and calcination of natural or synthetic polymers [S. Lei et al, Carbon, 2010, 48, 2644-2646; S. Zhang et al., New Carbon Materials, 2010, 25, 9-14]. On the other hand, graphitic carbon foams are generally prepared by foaming of coal, coal tar pitch and petroleum pitch followed by high temperature calcination and graphitization [M. Wang et al., Carbon, 2008, 46, 84-91; Z. Min et al., New Carbon Materials, 2007, 22, 75-79]. The graphitized porous carbon has high conductivity, well-aligned crystalline structure and good thermal stability.
All these methods for preparing RVC, non-graphitic carbon foams and graphitic carbon foams use different raw materials (precursors) and different synthetic conditions. For example, the first pitch based macroporous graphite foam was developed by Oak Ridge National Laboratory (ORNL) in 1997. Klett et al. [Carbon, 2000, 38, 953-973 and U.S. Pat. No. 6,033,506] found that the effective thermal conductivity of graphite foam was more than 150 W/m·K which was higher than the value of aluminium foam (ca. 2-26 W/m·K). On the other hand, the density of the graphite foam was 0.2-0.6 g/cm3 which was only ⅕ of that of aluminium foam. This macroporous carbon foam developed by ORNL is believed to be less expensive and easy to fabricate than the traditional foams. But this graphite foam only has a high thermal conductivity in a certain direction and it also has very high pressure drop due to the small scale pores and complex structure of the foam [A. G. Straatman et al., J. Engineering for Gas Turbines and Power, 2007, 129, 326-330].
WO2007/076469 describes a method for preparing a graphitic macroporous carbon foam with improved graphitizability by introducing a graphitization promoting additive into the carbon foam. However, high graphitization temperatures, i.e. between 2000 and 2600° C., are required.
In addition to that, the syntheses of macro/mesoporous silica and carbon monoliths have been explored by several authors [S. Alvarez and A. B. Fuertes, Materials Letters, 2007, 61, 2378-2381; H. Maekawa et al., Advanced Materials, 2003, 15, 591-596]. The first ordered mesoporous carbon-silica composite monoliths with macroporous architecture by using polyether polyol-based polyurethane (PU) foam as a sacrificial template was achieved by Xue et al [Chunfeng Xue et al, Advanced Functional Materials, 2008, 18, 3914-3921].
Based on the above process for obtaining ordered mesoporous carbon-silica composite monoliths with macroporous architecture, Xue et al. (Nano Research, 2009, 2, 242-253) also discloses a process for the synthesis of hierarchically porous carbon foams with ordered meso-structure that comprises the use of a macroporous monolithic template of polyurethane (PU) foam which is coated with an ethanol solution containing the carbon precursor (e.g. resol) and a triblock copolymer (e.g. Pluronic F127). After self-assembly of the carbon precursor and the copolymer in the PU foam, solvent evaporation is carried out according to a process known as EISA (evaporation induced self-assembly), followed by thermopolymerization, calcination and carbonization to yield the hierarchically porous carbon foam. However, the EISA method is not suitable for the up-scaling due to the need for large surface substrate discs and long-time solvent evaporation.
In spite of the hierarchically porous carbons described in the art, graphitized macroporous carbon foams with ordered mesopores on the walls have not yet been reported.